Ablation till: Loose, permeable till deposited during the final downwasting of glacial ice.

Acre: The unit of measure most typically used to describe land area in the United States. An acre is equivalent to 43,560 square feet and is about 9/10 the size of a football field.

Aeration, soil: The exchange of air in soil with air from the atmosphere. The air in a well aerated soil is similar to that in the atmosphere; the air in a poorly aerated soil is considerably higher in carbon dioxide and lower in oxygen.

Alluvium: Material, such as sand, silt, or clay, deposited on land by streams.

Anhydrous ammonia: An efficient and widely used source of nitrogen fertilizer for corn production. It is a chemical made up of one part nitrogen and three parts hydrogen. When used as an agricultural fertilizer, it is compressed into a liquid and is stored in specially designed pressurized tanks. Anhydrous means without water and consequently, when anhydrous ammonia comes in contact with any moisture, the water and ammonia rapidly combine. When injected into the soil, the liquid ammonia expands into a gas and is readily absorbed in the soil.

Ammonium Nitrate: A form of dry nitrogen fertilizer that is 34% nitrogen, by weight. It is produced by reacting anhydrous ammonia with nitric acid. When dissolved in water, the ammonium and nitrate fractions disassociate. The nitrate fraction remains dissolved in the soil water. The ammonium fraction becomes bound to negatively charged soil particles. Both the ammonium and nitrate fractions are available for direct plant uptake and neither form is subject to appreciable volatilization losses. The volatilization losses from surface applied ammonium nitrate are therefore usually quite small, especially compared to urea-based fertilizer. An advantage of ammonium-nitrate fertilizers (see also Urea) over anhydrous ammonia is that it can be broadcast as a dry product to the soil surface whereas ammonia must be injected into the soil to prevent vaporization. Broadcast application is faster and less expensive than injection.

Bedrock: The solid rock that underlies the soil and other unconsolidated material or that is exposed at the surface.

Board foot: A unit of measure of the wood in lumber, logs, or trees. The amount of wood in a board 1 foot wide, 1 foot long, and 1 inch thick.

Bottom land: The normal flood plain of a stream, subject to flooding.

Breast height: An average height of 4.5 feet above the ground surface; the point on a tree where diameter measurements are ordinarily taken.

Brush management: Use of mechanical, chemical, or biological methods to make conditions favorable for reseeding or to reduce or eliminate competition from woody vegetation and thus allow understory grasses and forbs to recover.  Brush management increases forage production and thus reduces the hazard of erosion.

Bushel: A unit of dry volume typically used to quantify crop yields. One bushel is equivalent to 32 quarts or 2,150.42 cubic inches. A bushel is often used to represent the weight of a particular crop; for example, one bushel of No. 2 yellow shelled corn at 15.5% moisture content weighs 56 lb.

Center Pivot: A type of irrigation system that consists of a wheel-driven frame that supports a series of sprinkler nozzles. The frame rotates about a central point to distribute water over a large circular area.

Chemical treatment: Control of unwanted vegetation through the use of chemicals.

Chiseling: Tillage with an implement having one or more soil-penetrating points that shatter or loosen hard, compacted layers to a depth below normal plow depth.

Chisel plow: Large curved shanks to penetrate and stir the soil without inverting a soil layer. Chisel plows cause less residue disturbance than moldboard plows and are often used in conservation tillage systems. Large chisel plows can exceed 50 feet in width.

Clay: As a soil separate, the mineral soil particles less than 0.002 millimeter in diameter.  As a soil textural class, soil material that is 40 percent or more clay, less than 45 percent sand, and less than 40 percent silt.

Claypan: A slowly permeable soil horizon that contains much more clay than the horizons above it. A claypan is commonly hard when dry and plastic or stiff when wet.

Clearcut: A method of forest harvesting that removes the entire stand of trees in one cutting.

Clod: A compact, coherent mass of soil of variable size, typically produced by plowing, digging, or other mechanical means, especially when these activities take place in areas where the soils are too wet or too dry.

Closed depression: A low area completely surrounded by higher ground and having no natural outlet.

Combines: Machines used to harvest grain and seed crops.   The major functions performed by a combine include cutting and/or gathering, feeding, threshing, separating, cleaning, and grain handling operations on-the-go in the field.   Most all are self-propelled, receiving power to perform all of the previously listed operations and traction from a diesel engine.   The combine is often the most expensive farm machine used in grain or row crop production and some can harvest a thirty-foot swath of crop in a single pass.

Conservation cropping system: Growing crops in combination with needed cultural and management practices. In a good conservation cropping system, the soil-improving crops and practices more than offset the effects of the soil-depleting crops and practices.  Cropping systems are needed on all tilled soils.  Soil-improving practices in a conservation cropping system include the use of rotations that contain grasses and legumes and the return of crop residue to the soil.  Other practices include the use of green manure crops of grasses and legumes, proper tillage, adequate fertilization, and weed and pest control.

Conservation tillage: A tillage system that does not invert the soil and that leaves a protective amount of crop residue on the surface throughout the year.

Contour stripcropping: Growing crops in strips that follow the contour. Strips of grass or close-growing crops are alternated with strips of clean-tilled crops or summer fallow.

Corn Belt: The area of the United States where corn is a principal cash crop, including Iowa, Indiana, most of Illinois, and parts of Kansas, Missouri, Nebraska, South Dakota, Minnesota, Ohio, and Wisconsin.

Cover crop: A close-growing crop grown primarily to improve and protect the soil between periods of regular crop production, or a crop grown between trees and vines in orchards and vineyards.

Cropping system: Growing crops according to a planned system of rotation and management practices.

Crop residue management: Returning crop residue to the soil, which helps to maintain soil structure, organic matter content, and fertility and helps to control erosion.

Delta: A body of alluvium having a surface that is nearly flat and fan shaped; deposited at or near the mouth of a river or stream.

Depression: A low area in a field where surface drainage away from the area does not occur.

Depth, soil: Generally, the thickness of the soil over bedrock.  Very deep soils are more than 60 inches deep over bedrock; deep soils, 40 to 60 inches; moderately deep, 20 to 40 inches; shallow, 10 to 20 inches; and very shallow, less than 10 inches.

Disk Harrow (or Disk): An implement that uses steel blades to slice through crop residues and soil. Disk blades are mounted in groups or gangs that rotate as they move forward through the soil. Front gangs move soil toward the outside of the disk while rear gangs move soil back toward the center of the disk. A disk can be used for primary or secondary tillage.

Drainage class: Refers to the frequency and duration of wet periods under conditions similar to those under which the soil formed. 

Drills: An implements used to plant crops in closely spaced rows (typically four to ten inches); drills are commonly used for cereal crops such as wheat and can be used to plant soybeans. Grain drills are typically equipped with disks to open a small trench in the soil, a metering system to deliver a measured, controlled amount of seed to drop tubes which guide the seed to the seed trench. There must be some means (wheels or drag chains) of gently closing the seed trench with soil to cover the seeds.

Fallow: Cropland left idle in order to restore productivity through accumulation of moisture.

Feed Grain: Any of a number of grains used for livestock or poultry feed. Corn and sorghum are feed grains.

Fertility, soil: The quality that enables a soil to provide plant nutrients, in adequate amounts and in proper balance, for the growth of specified plants when light, moisture, temperature, tilth, and other growth factors are favorable.

Field Cultivator: An implement used to perform secondary tillage operations such as seedbed preparation and weed eradication. Field cultivators are equipped with steel shanks that are typically spring mounted to permit the shank to move within the soil and shatter clods. Field cultivators are constructed similarly to chisel plows, but are built more lightly.

Field moisture capacity: The moisture content of a soil, expressed as a percentage of the ovendry weight, after the gravitational, or free, water has drained away; the field moisture content 2 or 3 days after a soaking rain.

Fine textured soil: Sandy clay, silty clay, or clay.

Flood plain: A nearly level alluvial plain that borders a stream and is subject to flooding unless protected artificially.

Flowering: This is the stage when the crop starts flowering. In corn, tassel emergence and pollen shedding takes place at this stage. Two to three days after pollen shedding, silk emergence takes place. At this stage, typically occurs 51-56 days after planting the corn seed, pollination between silks (female) and tassels (male) takes place.

Forage Crop: Annual or perennial crops grown primarily to provide feed for livestock. During harvesting operations, most of the aboveground portion of the plant is removed from the field and processed for later feeding.

Grain Carts: Tractor-drawn implements used to shuttle grain from combines to hauling vehicles or to grain receiving facilities. Grain carts are usually equipped with high-flotation tires or rubber tracks to attempt to minimize soil compaction in the field. The capacity of such carts can exceed 1,000 bushels (equivalent to 56,000 lb of shelled corn or 60,000 lb of soybeans).

Grassed waterway: A natural or constructed waterway, typically broad and shallow, seeded to grass as protection against erosion. Conducts surface water away from cropland.

Green manure crop (agronomy): A soil-improving crop grown to be plowed under in an early stage of maturity or soon after maturity.

Ground water: Water filling all the unblocked pores of the material below the water table.

Hardpan: A hardened or cemented soil horizon, or layer.  The soil material is sandy,  loamy, or clayey and is cemented by iron oxide, silica, calcium carbonate, or other substance.

Head out: To form a flower head.

High-residue crops: Such crops as small grain and corn used for grain.  If properly managed, residue from these crops can be used to control erosion until the next crop in the rotation is established. These crops return large amounts of organic matter to the soil.

Impervious soil: A soil through which water, air, or roots penetrate slowly or not at all. Not soil is absolutely impervious to air and water all the time.

Infiltration: The downward entry of water into the immediate surface of soil or other material, as contrasted with percolation, which is movement of water through soil layers or material.

Inputs: The basic elements necessary for agricultural production.  These primarily consist of seed, fertilizer, and crop chemicals such as herbicides, insecticides, and fungicides applied as-needed.  Fuel expenses are frequently consider and input cost as well.

Intake rate: The average rate of water entering the soil under irrigation. Most soils have a fast initial rate, the rate decreases with application time.

Irrigation: Application of water to soils to assist in production of crops. Some methods of irrigation include: basin, border, controlled flooding, corrugation, drip or trickle, furrow, sprinkler, subirrigation and wild flooding.

Loam: Soil material that is 7 to 27% clay particles, 28 to 50% silt particles, and less than 52% sand particles.

Low-residue crops: Such crops as corn used for silage, peas, beans, and potatoes. Residue from these crops is not adequate to control erosion until the next crop in the rotation is established. These crops return little organic matter to the soil.

Muck: Dark, finely divided, well decomposed organic soil material. The most highly decomposed of all organic soil material. Muck has the least amount of plant fiber, the highest bulk density, and the lowest water content at saturation of all organic soil material.

Moldboard plow: A large frame that is equipped with a series of "bottoms," each of which consists of a steel coulter to slice through residue followed closely by a steel share that cuts the soil and an attached moldboard that is used to raise and turn over the cut slice of soil.

Nitrogen: Nitrogen is one of sixteen chemical elements essential for plant growth. Green plants must be able to assimilate all sixteen nutrients to carry on cell growth and metabolic activities. Plants get oxygen , carbon, and hydrogen from the air and water, the other nutrients are taken from the soil. Nitrogen, phosphorus, potassium, are sometimes referred to as the primary nutrients while calcium, magnesium, and sulfur are referred to as secondary nutrients. Another seven essential nutrients are taken up in much smaller quantities and are collectively referred to as micro-nutrients. These are: boron, chlorine, copper, iron, manganese, molybdenum, and zinc.

Natural nitrogen: Some plants "make their own nitrogen". If a legume (i.e., soybeans, alfalfa, clovers) is colonized by certain strains of Rhizobium bacteria, nodules will form on the plant roots where the bacteria live and reproduce. Within these nodules, a symbiotic relationship develops between the bacteria and the host plant. The bacteria utilize plant sugars as a source of energy and in turn "fix" nitrogen, converting nitrogen gas into forms that can be used by the plant. Once nodules form, the plant usually receives all of the nitrogen necessary for growth from that "fixed" by the bacteria. Other crops, including all grass crops (e.g., corn, sorghum, wheat, forage grasses, etc.) and non-leguminous broadleaf crops (e.g., sunflowers, potatoes, sugar beets, cotton, etc.) are not colonized by nitrogen fixing bacteria and therefore must obtain the nitrogen they need from the soil.

No-till: A conservation tillage method where no tillage is done at all and seeds are placed directly into the previous season's crop residue.

Nutrient, plant: Any element taken in by a plant essential to its growth. Plant nutrients are mainly nitrogen, phosphorus, potassium, calcium, magnesium, sulfur, iron, manganese, copper, boron, and zinc obtained from the soil can carbon, hydrogen, and oxygen obtained from the air and water.

Organic matter: Plant and animal residue in the soil in various stages of decomposition. The content of organic matter in the surface layer id described as follows: low—0.5 to 1%, moderate—1 to 2%, high—4 to 8%.

Peat (fibric soil material): The least decomposed of all organic soil material.  Peat contains a large amount of well preserved fiber that is readily identifiable according to botanical origin. Peat has the lowest bulk density and the highest water content at saturation of all organic soil material.

Percolation: The movement of water through the soil.

Permeability: The quality of the soil that enables water or air to move downward through the profile. The rate at which a saturated soil transmits water is accepted as a measure of this quality.

Planters: An implement used to plant row crops (typically in row spacings ranging from 10 to 40 inches).   Planters open a seed trench, meter seeds one-at-a-time, drop seeds into the seed trench, and gently cover the seed.   Some planters can cut through residues and till a small strip of soil in each row at the time of planting.   Planters can also be equipped to apply fertilizer, pesticides, and herbicides during planting.   Planters come in sizes as large as sixty feet wide - that is twenty-four rows with a typical 30-inch row spacing, or thirty-six rows with a narrower 20-inch row spacing.

Plowpan: A compacted layer formed in the soil directly below the plowed layer.

Ponding: Standing water on soils in closed depressions. Unless the soils are artificially drained, the water can be removed only by percolation or evaporation.

Postemergence: Refers to the timing of pest control operations. Postemergence operations are accomplished during the period subsequent to the emergence of a crop from the soil and must be completed prior to point at which crop growth stage prohibits in-field travel (unless alternative application means – aerial or irrigation-based – are used).

Productivity, soil: The capability of a soil for producing a specified plant or sequence of plants under specific management.

Profile, soil: A vertical section of the soil extending through all its horizons and into the parent material.

Potential rooting depth: Depth to which roots could penetrate if the content of moisture in the soil were adequate. The soil has no properties restricting the penetration of roots to this depth.

Proper grazing use: Grazing at an intensity that maintains enough cover to protect the soil and maintain or improve the quantity and quality of the desirable vegetation. This practice increases the vigor and reproduction capacity of the key plants and promotes the accumulation of litter and mulch necessary to conserve soil and water.

Reaction, soil: A measure of acidity or alkalinity of a soil, expressed in pH values. A soil that tests to pH 7.0 is described as precisely neutral in reaction because it is neither acid nor alkaline.

Regeneration: The new growth of a natural plant community, developing from seed.

Rill: A steep-sided channel resulting from accelerated erosion. A rill generally is a few inches deep and not wide enough to be an obstacle to farm machinery.

Rill irrigation: An intentionally created rill designed to carry water from a source such as a stream or pond to a field so that soil moisture can be increased through natural percolation without mechanically disbursing the water.

Root zone: The part of the soil that can be penetrated by plant roots.

Row Crop: Agricultural crop planted, usually with mechanical planting devices, in individual rows that are spaced to permit machine traffic during the early parts of the growing season.

Sand: As a soil separate, individual rock or mineral fragments from 0.05 millimeters to 2.0 millimeters in diameter. Most sand grains consist of quartz. As a soil textural class, a soil that is 85 percent or more sand and not more than 10 percent clay.

Saturation: Wetness characterized by zero or positive pressure of the soil water. Under conditions of saturation, the water will flow from the soil matrix into an unlined auger hole.

Sawlogs: Logs of suitable size and quality for the production of lumber.

Scarification: The act of abrading, scratching, loosening, crushing, or modifying the surface to increase water absorption or to provide a more tillable soil.

Side-dress: The application of fertilizer after the crop has started to grow when it is needed most by the plant.

Silt: As a soil separate, individual mineral particles that range in diameter from the upper limit of clay (0.002 millimeters) to the lower limit of very fine sand (0.05 millimeter). As a soil textural class, soil that is 80 percent or more silt and less than 12 percent clay.

Slope: The inclination of the land surface from the horizontal. Percentage of slope is the vertical distance divided by horizontal distance, then multiplied by 100. Thus, a slope of 20% is a drop of 20 feet in 100 feet of horizontal distance.

Soil: A natural, three-dimensional body at the earth’s surface. It is capable of supporting plants and has properties resulting from the integrated effect of climate and living matter acting on earthy parent material, as conditioned by relief and by the passage of time.

Soil quality: The fitness of a specific kind of soil to function within its surroundings, support plant and animal productivity, maintain or enhance water quality and air quality, and support human health and habitation.

Soil separates: Mineral particles less than 2 millimeters in equivalent diameter and ranging between specified size limits. The names and sizes, in millimeters, of the three primary separates are as follows: sand—2 to 0.05 millimeters, silt—0.05 to 0.002 millimeters, and clay—less than 0.002 millimeters.

Solum:  The upper part of a soil profile. Generally, the characteristics of the material in these horizons are unlike those of the material below the solum. The living roots and plant and animal activities are largely confined to the solum.

Sprayer: An implement or vehicle used to apply liquid crop chemicals, most often herbicides, and increasingly, fertilizers.  Sprayers typically include a tank, pump, plumbing, valves, a boom, and nozzles. Sprayers can be mounted on a tractor or other implement, pulled by a tractor, self-propelled, or mounted on airplanes or helicopters.

Spreader: An implement or vehicle used to apply dry crop chemicals, most often fertilizers. Spreaders typically include a bed, conveyor, and either a set of spinning disks to distribute material over a wide area or a pneumatic system to push material through openings in a boom for distribution on the ground. Spreaders can be mounted on a tractor, pulled by a tractor, self-propelled, or mounted on airplanes.

Sprinkler Irrigation: With sprinkler irrigation, water is sprayed through the air from pressurized nozzles, and falls like rain on the crop. Variable-flow irrigation sprinkler heads improve the precision of water applications.

Stubble mulch: Stubble or other crop residue left on the soil or partly worked into the soil. It protects the soil from wind erosion and water erosion after harvest, during preparation of a seedbed for the next crop, and during the early growing period of the new crop.

Subsoil: The part of the solum below plow depth.

Subsurface drainage: Removes excess water from the soil profile, usually through a network of perforated tubes installed 2 to 4 feet below the soil surface. These tubes are commonly called "tiles" because they were originally made from short lengths of clay pipes known as tiles. Water would seep into the small spaces between the tiles and drains away.

Surface drainage: The removal of water that collects on the land surface. Many fields have low spots or depressions where water ponds. Surface drainage techniques such as land leveling, constructing surface inlets to subsurface drains, and the construction of shallow ditches or waterways can allow the water to leave the field rather than causing prolonged wet areas.

Surface Irrigation: With surface irrigation, water flows directly over the surface of the soil. The entire surface can be flooded (most often used for crops that are sown, drilled or seeded) or the water can be applied through furrows between the rows (for row crops).

Surface layer: The soil ordinarily moved in tillage, or its equivalent in uncultivated soil, ranging in depth from 4 to 10 inches.

Tasseling: A condition when the tassel-like male flowers emerge.

Texture, soil: The relative proportions of sand, silt, and clay particles in a mass of soil. The basic textural classes, in order of increasing proportion of fine particles, are sand, loamy sand, sandy loam, loam, silt loam, silt loam, silt, sandy clay loam, clay loam, silty clay loam, sandy clay, silty clay, and clay.

Tile or tiling: Generally, corrugated plastic tubing with small perforations to allow water entry buried 2 to 4 feet below the surface. When the water table in the soil is higher than the tile, water flows into the tubing, either through holes in the plastic tube or through the small cracks between adjacent clay tiles. This lowers the water table to the depth of the tile over the course of several days. Drain tiles allow excess water to leave the field, but once the water table has been lowered to the elevation of the tiles, no more water flows through the tiles. In most years, drain tiles are not flowing between June and October.

Tillage: Prior to planting, the soil is prepared, by some form of tillage or chemical "burn-down" to kill the weeds in the seedbed that would crowd out the crop or compete with it for water and nutrients. Tillage methods can be divided into three major categories, depending on the amount of crop residue they leave on the surface. Residue slows the flow of runoff that can displace and carry away soil particles. Conventional tillage uses a moldboard plow for primary tillage followed by several secondary tillages and mechanical cultivation after the crops are up. Now about two-thirds of row crops are planted without use of the moldboard plow and mechanical cultivation is often limited to one, or no operations. Reduced tillage is usually done with a chisel plow and leaves 15% to 30% residue coverage on the soil. Conservation tillage leaves at least 30% residue coverage on the soil. Conservation tillage methods include no-till, where no tillage is done at all and seeds are placed directly into the previous season's crop residue; strip-till, in which only the narrow strip of land needed for the crop row is tilled; ridge till; and mulch till.

Tilth, soil: The physical condition of the soil as related to tillage, seedbed preparation, seedling emergence, and root penetration.

Topsoil: The upper part of the soil, which is the most favorable material for plant growth. It is ordinarily rich in organic matter and is used to top-dress road banks, lawns, and land affected by mining.

Trace elements: Chemical elements, for example, zinc, cobalt, manganese, copper, and iron in soils in extremely small amounts.  They are essential to plant growth.

Trickle/Drip Irrigation: Trickle or drip irrigation supplies water directly onto or below the soil surface through emitters that control water flow.

Urea: A dry pelletized form of nitrogen fertilizer that is popular as a nitrogen fertilizer because of its relatively high nitrogen content (46% of the total weight is nitrogen), good storage and handling properties, and widespread availability. Urea is produced by combining anhydrous ammonia with carbon dioxide. An advantage of urea over anhydrous ammonia is that it can be broadcast as a dry product to the soil surface whereas ammonia must be injected into the soil to prevent vaporization. Broadcast application is faster and less expensive than injection

Wilting point: The moisture content of soil, on an ovendry basis, at which a plant (specifically a sunflower) wilts so much that it does not recover when placed in a humid, dark chamber.

Windbreaks: A row of trees or shrubs that protect soil from wind erosion.